Inhibition of metal corrosion



Feb. 3, 1970 G. R. WEBER INHIBITION OF METAL CORROSION 3 Sheets-Sheet 1 Filed Oct. 25, 1967 1970 G. R. WEBER 3,493,42i

INHIBITION OF METAL CORROSION Filed Oct. 25, 1967 3 Sheets-Sheet 3 Feb. 3, 1970 s. R. WEBER INHIBITION OF METAL CORROSION 3 Sheets-Sheet 5 Filed Oct. 25, 1967 T nqE.

fi 1 D l 1 3,493,421 INHIBITION OF METAL CORROSION George R. Weber, Cincinnati, Ohio, assignor to National Distillers and Chemical Corporation, New York, N.Y., a corporation of Virginia Filed Oct. 25, 1967, Ser. No. 678,492 Int. Cl. Bb 13/06; B05c 7/00 U.S. Cl. 117-94 8 Claims ABSTRACT OF THE DISCLOSURE A process for inhibiting metal corrosion according to which there is applied to a metal object subject to corrosion a composition selected from the group comprising terramycin, neomycin or mandelamine.

This invention relates to the inhibition of metal corrosion and, more particularly, to a novel technique for preventing the type of metal corrosion that is due to the action of autotrophic agents having more resistance to destruction than conventional microorganisms. The particular type of corrosion referred to here is not caused by conventional microorganisms. It may be readily demonstrated, for example, by aseptically placing aluminum alloy (type 565) wires (previously autoclaved at 121 C. for 2 hours) on a sterile medium such as formula 993'-2038 or 108933 referred to hereinafter. The treatment of the wires and of the media is such as to destroy conventional biological agents including the more resistant spore types. The corrosion which results thus results from culturable autotrophic agents far more resistant than conventional microorganisms.

It has been known that under certain conditions, as for example in the burial of iron pipes and the like, corrosion is brought about by bacterial or biochemical reaction. In US. Patent 2,769,921 a form of corrosion which affects well casings has been discussed. That form of corrosion has been understood to be indirectly caused by so-called sulphate-reducing bacteria which exist under anaerobic conditions and reduce naturally-occuring sulphates to hydrogen sulphide, the hydrogen sulphide, in turn, attacking the iron to form iron sulphide. As is also noted in the patent, in other instances corrosion may be brought about by the presence of so-called iron bacteria. Other prior art knowledge relating to microbiological corrosion is contained for example, in US. Patent 2,979,377.

Completely unrelated to the foregoing examples of microbiological metal corrosion prevention is the discovery upon which the present invention is based. Such discovery represents a complete departure from what has been known before, its context or milieu being totally different from that of the previous knowledge. It has in common with the prior art examples given, only the practical objective of inhibiting corrosion which results from activity of culturable agents. Sulphate-reducing bacteria and iron bacteria referred to in the previouslycited patents are conventional microorganisms and are destroyed by normal autoclaving techniques such as 121 C. for 20 minutes. The corrosion producing agents about which this invention is concerned, are not destroyed by these usual autoclaving techniques. In the aluminum alloy metal they have, in fact, survived autoclaving at 121 C. for periods greatly in excess of that (20 or 30 minutes) required to destroy conventional microorganisms, such a s 24 and 48 hours of continuous autoclaving. The present invention rests upon the discovery that autotrophic agents are associated with many common forms of ordinary metal corrosion.

It is considered most useful at this juncture to note that autotrophic microorganisms are those which build 3,493,421 Patented Feb. 3, 1970 their own nutritive substances by photosynthesis or chemosynthesis. The organisms or agents that have been found to be associated with ordinary metal corrosion, so resemble the aforesaid autotrophic microorganisms in their nutritive requirements that they have been given the same general designation, but it is recognized that they have characteristics which have not been attributed to conventional autotrophic microorganisms. In extended studies of these agents, however, many of the characteristics do resemble those of conventional microorganisms. For example, characteristic spherical fruiting bodies were regularly observed in and about corroding metals by means of an ordinary light microscope. The morphology of the fruiting body varies from strain to strain. Pursuant to these studies these agents were subsequently cultured on media largely inorganic. Further studies under the electron microscope revealed that the spherical fruiting bodies were packed with tiny virus size spirals. The electron dilfraction pattern indicates that these fruiting bodies are not inorganic; a diffraction pattern similar to carbon is detected.

Although infrared analysis did not show the presence of organic matter, these microorganisms or agents behave like living organisms or autotrophs in that they appear to go through similar stages, i.e., through a vegetative stage and the aforesaid fruiting body stage.

Whatever their precise nature, these agents have been found in the corrosion of metal such as aluminum, iron, copper and zinc. In order to determine their effects these agents have been cultured so that additional analysis might be made. Further, it has been found that some agents of the cultured groups are able to initiate corrosion in an aluminum alloy.

As a result of the initial discovery that the aforesaid autotrophic agents are associated with metal corrosion, studies were carried out to determine what specific chemicals might be useful from a practical standpoint in attacking such agents to inhibit their noxious effects. Various media were tried for culturing these agents and a development of a medium for supporting sufiicient heavy growth of these agents made it possible to check the inhibition of these cultures by antimicrobial agents. It was found that certain antimicrobial agents, especially terramycin, neomycin and mandelamine were most efficacious in such inhibition.

In a nutshell, what these discoveries add up to is that certain types of corrosion in metals can readily be prevented or at least substantially mitigated by the use of certain chemicals applied to these metals by various means so as to inhibit the autotrophic agents that are producing the corrosion.

Accordingly, a fundamental object of the present invention is to eliminate or substantially prevent the type of corrosion in metals that is produced by bacteria-like autotrophic agents.

The above object, as well as subsidiary objects, is fulfilled in accordance with the present invention by simply applying to the metal object which is subject to corrosion, a coating of the specific chemical, for example, the antimicrobial agents such as terramycin, neomycin and mandelamine. Of course, as the description proceeds it will be brought out that other antimicrobial agents can also be used, but that the above-noted antimicrobial agents have been found to be most effective by far.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.

FIGS. 111 are photomicrographs or electron micrographs of corrosion samples illustrating the development of autotrophic agents.

In order to ascertain definitely the relationship of the autotrophic agents to the corrosion found in typical metals such as aluminum, iron, copper and zinc, studies were conducted which involve the culturing of these autotropic agents. These studies will now be described to aid in appreciating the significance of the technique of the present invention to the problem of corrosion prevention.

It should be particularly noted here that re-inoculation studies give clearcut support to the view that the autotropic agents are associated with metal corrosion. In other words it has been clearly shown that these agents can be cultured from corrosion masses on to a suitable medium, transferred upon the medium free of the metal and re-inoculated onto non-corroded metal to initiate a similar type of corrosion. Several types of these agents, morphologically diiferent, are associated with corroding metals, some being very active corroders whereas others produce mild pitting. FIG. 9 shows heavy white corrosion which developed at one end of each of two aluminum wires. One wire was then reversed and the photograph made three days after the reversal clearly demonstrates the reinfection at a new location on the wire where no corrosion existed previously.

The general thesis of the studies which have been made is that the spherical bodies observed in corroding metals, particularly, in corroding aluminum alloys, are significant in metal corrosion. Culturing of these bodies was carried out so that their nature could be more precisely determined with the result that the corrosion in which they were participating could be exhibited.

Some 350 mineral formulations were studied as culture media. Tables I and II immediately below summarize some of the media formulations tested during these studies.

TABLE IA.MEDIA FORMULATIONS [Grams per 100 m1.] 1

Formulation No.

Chemical Formula Part A:

Dionized water (1111.) 50 Distilled water (1111.). 2 5O 2 50 2 50 2 50 2 50 2 50 Agar 2. 00 2. 00 2. 00 2.00 2 00 2 00 2. 00 Yeast Extract-.. 0. l5 0. 15 0. 15 0.15 0.15 0.50 Urea 0. 15 0.15 0.15 0.15 0. 15 0. 15 Autoclaved (121 (1.), min. 20 20 20 20 20 20 Part B:

Dionized water (1111.) 50 Distilled water (1111.). 2 50 2 50 50 2 50 2 50 2 50 M11804 H2O 0. 005 1. 255 0. 005 O. 005 0. 005 0. 005 0.01 0. 01 0. 01 0. 01 0.01 0.01 0.00325 Na2M0O 0. 00025 0. 00025 0. 00025 0. 00025 0. 00025 0. 00025 0. 00025 K103 0.000125 0.000125 0.000125 0.00012 0.000125 0. 000125 0. 000125 AlCla- 61120 0. 0025 0. 0025 0. 0025 0. 0025 0. 0025 0. 0025 0. 0025 (NaPO )u H 0. 025 0. 025 0. 275 0. 025 0. 025 0. 025 0. 025 C0804- 71120 0. 50 O. 50 2. 50 0. 50 0. 50 2. 50 0. 50 CuSO1- 5H2O 0 0125 0. 0125 0. 0125 0. 0125 0. 0125 0. 0125 0. 0125 M115 O1-7H 20 0.03 0.03 0.025 0.03 0.03 0. 03 0.03 KNO 0. 15 0. 15 0. 15 15 0. 15 0. 15 0. 15

Versene Fe Malachite green oxalate (101102020 1120 Rosanilin hydrochloride Autoclaved (121 0.), hrs Filtered (.01 micron) pH of finished medium (1 time) (2 times) (1 time) (1 time) 6. 0 4. 7 6. 3 6. 0 5 5. 9

{Trace concentrations were prepared from composite mixes. Weights recorded to several decimal places are included to show relative proportions used in making stocks and are not nitended to imply unusual accuracy.

2 Distilled water autoelaved 2 hours (121 C.)

Formulation No.

Chemical Formula 0032036 093-2037 9932038 993-235-1 993-235-2 9932353 903-235-4 993-235-5 Part A:

Deionized water (ml.) Distilled Water (1111.). 2 50 2 50 2 50 2 5O 2 50 2 50 2 50 2 50 Agar 2. 00 2. 00 2. 00 2. 00 2. 00 2. 00 2. 00 2. 00 Yeast Extract 0. 75 0. 0.25 0. 75 0. 25 0. 75 0.75 07 Urea O. 15 0. l5 0. 15 0. 15 0. 15 0. 15 0. 15 0. 15 Autoclaved (121 0.), min. 20 20 20 20 20 20 Part B:

Deionized water (1111.) Distilled water (ml.) 2 50 2 50 2 9 50 3 50 2 50 2 50 2 50 MnSO -HgO 0. 005 0. 005 0. 005 0. 005 0. 005 0. 005 0. 005 0. 005 95156 21120 0. 01 0. 01 O. 01 0. 01 0. 01 0. 01 0. 01 O. 01 A1 4 a i a NagMOO -2H O 0. 00025 0. 00025 0. 00025 0. 00125 0. 00025 0. 00025 0. 00025 0. 00025 K10 0. 000125 0. 000125 0 000125 0. 000125 0. 000125 0. 000125 0. 000125 0. 000125 0. 0025 0. 0025 0. 0025 0. 0025 0. 0025 0. 0025 0. 0025 0. 0025 0. 025 0. 025 0. 025 0. 025 0. 025 0. 025 0. 025 0. 025 0. 0125 0. 0125 O. 0125 0. 0125 O. 0125 0. 0125 0. 0125 0. 0125 0. 03 0. 03 0. 03 0. O3 0. 03 0. 03 0. 03 0. 03 0. 15 0. l5 0. 15 0. 15 0. 15 0. 15 0. 15 0. 15 O. 15 0. l5 0. 15 0. 15 0. 15 0. 15 0. l5 0. 15 0. 0025 0. 0025 0. 0025 0. 2005 0. 0025 O. 0025 0. 0025 O. 0025 NitzBrO7-H2O Versene Fen Malachite green oxalate 02CzO4-H2O Rosanilin hydrochloride Autoclaved (121 (3.), hr Filtered (.01 mieron) pH of finished medium 1 Trace concentrations were prepared from composite mixes. Weights recorded to several decimal places are included to show relative proportions used in making stocks and are not Intended to imply unusual accuracy.

2 Distilled water autoclaved 2 hrs. (121 C.). 3 1 hour.

N or15.131end parts A and B pour into sterile glassware.

TABLE II Media formulation No. 1089-3-3 Chemical formula: Grams r millilters per 100 ml.

Part A:

Deionized water 2 50 Agar 2.00 Yeast extract 0.25

Urea 0.15 Autoclaved (121 C.) min 20 Part B:

Deionized water 50 MnSO .H O 0.075 CaCl .2H O 0.01125 ZnCO 0.00275 NaMoO .2H O 0.000275 KIO 0.0001375 AlCl .6H O 0.00275 (NaPO 0.0375 CoSO .7H O 0.50025 CuSO .5H O 0.01375 KNO 0.15 NH Cl 0.075 Versene Fe 0.06 Malachite green oxalate 0.0005 NiSO .6I-I O 0.00025 V 0 0.00025 K Cr O 0.00025 SeO 0.00025 Na SiO .9I-I O 0.00025 ZrO(NO .2H O 0.00025 Na B O .10H O 0 00025 (NH C O .H O 0.01 Titanium potassium oxalate 0.0025 Ethyl oxalate 0.1

Autoclaved (121 C.) hr 1 pH of finished medium 3.3

Blend parts A and B; pour into sterile glassware.

1 Trace concentrations were prepared from composite mixes. Weights recorded to several decimal places are included to show relative proportions used in making stocks and are not intended to imply unusual accuracy.

-Deionized water me-autoclaved 2 hours (121 C.).

It will be noted that one of the principal ingredients of these mixtures is cobaltous sulphate which was used at a concentration of approximately 0.5%.

The type of body which has been cultured is indicated in FIG. 1 wherein is shown a piece of corrosion material which developed in a medium adjacent to an aluminum alloy Wire which had been autoclaved 24 hours at 120 C., 15 p.s.i.g. The medium upon which this corrosion developed is composed of two fractions, one of which is autoclaved for one hour and the other for 20 minutes. By proper lighting while photographing it was possible to detect the characteristic mulberry grouping or clusters of spheres.

Initial attempts were made to increase the quantity of culture in a liquid medium by agitation on a reciprocal shaker or by bubbling air through a fritted glass filter; but these techniques were not found to be effective. The most successful procedure was to culture on relatively dry surfaces. Petri dishes of media worked well and the particulate nature of the culture was readily demonstrated by inoculating only the first of six plates and thinning out the culture over successive plates with a sterile bent glass rod.

The culture shown in FIG. 2 was isolated from corroded aluminum and was successfully grown on a medium identified as 9701665. At this magnification (400x), which is the same as used in FIG. 1, the sizes of the individual spherical bodies are comparable. FIG. 3 which is an enlargement of FIG. 2 (1000 shows somewhat more detail of the fruiting bodies.

Throughout the culture studies undertaken, it has been apparent that some variation in morphology exists between diiferent strains. This is demonstrated by a comparison of FIGS. 3, 4 and 5. In FIG. 3, fruiting bodies are relatively flat and rough. FIG. 4 (1000 shows fruiting bodies from corroded zinc alloy which gives a smoother donut appearance. FIG. 5 (1000 shows fruiting bodies from corroded steel. Here, again, the diameter is of the same approximate order as in FIGS. 3 and 4, but the individual bodies have raised centers giving somewhat the appearance of tiny microbial colonies. FIG. 6 (1000 shows a culture isolated from corroded aluminum somewhat resembling the fruiting bodies in FIG. 3, but growing in masses of crystals. These cultures were isolated from three different corroded metals but these difierences in the morphology of the fruiting bodies do not necessarily represent only the metal from which they were isolated. Limited re-inoculation data suggest, for example, that a culture isolated from corroded steel may also be involved in aluminum corrosion.

By the use of an electron microscope there has been observed, in characteristic cultures producing fruiting bodies, tiny spiral units approximately Vs micron in length. For example, one culture (identified as 993126 27) was initially isolated from corroded steel and subsequently inoculated to non-corroded aluminum alloy wire. The aluminum wire corroded at the point of inoculation and the culture studied was an isolate from the point of corrosion. Several other cultures have also been studied under the electron microscope. One, identified as 993- 235-4 is the same isolate as referred to in FIG. 2 and 3, but with two subsequent sub-transfers in other culture media.

FIGS. 7A and 7B show this culture (993-2654) in electron micrographs at magnifications of 2926 and 10,920 respectively. These electron micrographs show the clustering effect of the spherical bodies, but no evidence of the aforenoted tiny spirals.

FIG. 8 shows electron micrographs at a magnification of 10,902 of another culture identified as 993-264-220. This culture was initially isolated from an aluminum alloy wire which corroded after being autoclaved 24 hours at C. The medium upon which this corrosion took place had been prepared in two fractions, one of which was autoclaved for one hour, and the other fraction for 20 minutes. There is the possibility that the culture may have persisted either in the Wire or the medium, but nevertheless corrosion developed. Two fruiting bodies are shown in FIG. 8, beginning to disintegrate, with some tiny spirals evident.

Although a great number of diiferent media were formulated and tested, it was found that the media identified as 993-203-8 and 108933 (see Tables I and II) proved to be the most satisfactory and the most reliable ones that were developed. It was possible on these media, for example, to show a dilution eflFect indicating a particulate nature of the culture, by placing a transfer loop of a culture on the first of six plates and thinning out through subsequent plates by smearing successively with a sterile bent glass rod.

It should be noted that infrared analyses were made of growth on the surfaces of standard slants. It was not possible by this method to detect the presence of organic material in the culture. Likewise it has not been possible to detect organic matter in the culture medium which in one case had 0.75% yeast extract. Indications are that the infrared method is not sufiiciently sensitive to detect organic material under these conditions.

INHIBITION BY ANTIMICROBIAL AGENTS In order to elucidate the nature of the autotrophic agents responsible for the corrosion encountered in the samples tested, the culture previously identified as 993- 264-20 was tested against 41 standard antimicrobial discs,

most of which were antibiotics. In accordance with this technique, plates of medium 993-2038 were heavily inoculated with the culture and uniformly smeared with a sterile bent glass rod. Paper discs containing the antimicrobial agents were then aseptically placed on the medium prior to any growth. After a suitable incubation period at about 30 C. the plates had developed a significant surface growth. Plates were checked initially at days and finally at 18 days. This growth was examined under a microscope and characteristic fruiting bodies were present throughout. In some areas, however, surrounding specific discs inhibition of growth was very distinctly evident. Table III shows a summary of these results.

TABLE TIL-EFFECT OF ANTIMICROBIAL AGENTS ON CULTURE 993-26420, FRUITING BODY TYPE ISOLATED FROM CORRODED ALUMINUM [Medium 993-203-8, pH 6.2, final reading after 18 days, approx. 0.]

Difco. paper Area of disc inhibition No. in sq. mm.

Name of antimicrobial No. agent Remarks Polymyxin B Terramycin Very slight efiect. Slight effect. Very slight effect.

Declomycin Aureomycin Streptomycin Dihydrostreptomycin. Triple Sulla Baeitracin Tetracycline Peniciliin Gantrisin Iso Nicotirric acid hydrezide.

Triburon 14 Mycostatim. l5 Phenethicillin. 16 I Mandelamine eilcct. Ristoectin Chloromycetin Kanomyein. I Nalidixie Acid Coly-Myein. Sulfathiazole.

30 Very slight efi'ect.

170 Second best.

Sulfadiazine Neomycin Erythromycin- Sulfamerazino. Furadantin. 29 Thiosulfil.

30- Vanomycin- 31 Gantanal.

32 Spiramycin 33 Methicillim 37. Oxacillin 38 Viomycin- 40. Sulfamethoxy pyridazine.

41 Para amino salicylic 1 Total area of circle minus area of disc.

It will be noted that for this particular culture the most effective inhibitor was mandelamine (Difco No. 6743) in which case a clear zone of 590 square mm. resulted. This represents an overall zone diameter of 28 mm. with a very distinct clear border with no growth around the disc. Neomycin (Difco. No. 6173) appeared to be next best in that it had a zone area of 170 square mm. exclusive of the disc. The overall zone diameter was 16 mm. with a disc of 6 mm. in diameter. Eight other antimicrobial agents showed a limited effect as indicated in Table III.

In addition to checking the phenomenon of inhibition with culture 993-264-20, the phenomenon was also checked with two other cultures, identified as 993-266-11 and 993-264-13, each of which was previously isolated from corroded aluminum. The results were that each of these strains is inhibited by mandelamine and neomycin, but the more pronounced effect is obtained with neomycin rather than mandelamine. Moreover, culture 993- 26641 showed limited sensitivity to 5 other antimicrobial agents and culture 993264-l3 showed limited sensitivity to 14 others. In these studies there appears to be no question as to the sensitivity of these cultures to antimicrobial agents. The degree of inhibition may vary slightly due to the amount of inoculum or other factors.

APPLICATION OF FINDINGS From the results of the culture studies described hereinafore it became apparent that agents readily culturable from corroding metals, particularly aluminum alloy, could, in fact, be inhibited by antimicrobial agents, many of which were antibiotics. With conventional microorganisms, there is exhibited a high degree of specificity for antimicrobial agents such that one such agent which will inhibit one culture may be ineffective against another. Since differences in morphology exist in these autotrophic agents, a similar specificity of action of antimicrobial agents was expected. Thus, while terramycin appeared to be less effective against culture strain 993-26420 (Table III), when applied directly to the wire against a residual agent of another strain, it developed that terramycin was exceedingly eflfective.

To apply the findings to test the prevention of corrosion of metal, aluminum alloy wires (type 568) were stripped from commercially available screen and cut itno 5 centimeter lengths. These were autoclaved at 121 C. for 2 hours and dried in an oven under aseptic conditions. This sterilizing procedure is far in excess of what is commonly employed in bacteriological work (20 minutes) or surgical equipment (30 minutes) and is more than sufficient to destroy known microorganisms. Petri plates of media previously described largely inorganic, (993-203-8) and (1089-3-3) were prepared and maintained under aseptic conditions. Aluminum alloy wires, autoclaved as above, were aseptically placed upon the medium. Residual contamination surviving the two hours of autoclaving was such that each S-centimeter length averaged between 1 and 2 corrosion spots. On medium 1089-3-3, for example, heavy white corrosion masses were produced within 24 hours at room temperature (2325 C.) and these masses progressed along the wire, to erode away the metal within a few days, generally spreading across most or all of the wire.

Neomycin sulfate applied directly to the corrosion mass effectively arrested it and held it in check for a period of at least 2 weeks. Mandelamine proved to be effective only against a pitting type of corrosion and not effective against the most severe massive type. Terramycin containing an equal amount of a cationic surface active agent such a benzethonium chloride (iso-octylphenoxy-ethoxyethyl dimethyl benzyl ammonium chloride) was the most effective of those commercially available products tested when applied directly to corroding aluminum alloy wires. It effectively arrested massive severe aluminum corrosion and held it in check for at least two weeks whereas controls were heavily eroded away during this period.

Since antibiotics are produced largely by fungi, a fungus (1089-42B) was developed which grows readily on medium 1089-3-3 and which completely inhibited corrosion of aluminum alloy wires. Control tests in which aluminum wires (autoclaved at 121 C. for 2 hours) were placed on medium l08933 showed corrosion masses beginning to develop in about six hours. After 24 hours, each wire was actively corroding at one or two 10- cations, due to natural contamination from the wire. However, similar experiments in which the fungus was permitted to grow in the medium and produce antibiotics prior to the introduction of the aluminum alloy wires showed no corrosion whatsoever after 15 days. In tests in which wires were placed on the medium after the fungus was started but before it had produced maximum antibiotics, the wires were only partially protected. On the same plates after more antibiotics had been produced, aluminum alloy wires remained completely protected from corrosion. Photograph 10 is one of these experiments with wires corroding. Corrosion developed overnight and the photograph was made after 9 days. Photograph 11 shows 5 wires placed on the medium after the fungus had produced sufiicient antibiotic. No corrosion developed after 16 days.

EXAMPLE I Five aluminum alloy wires (type 568, 5 centimeters in length) were autoclaved 2 hours at 121 C. and placed on the surface of a Petri dish of agar medium l08933. Incubation was at room temperature (2325 C.). Observations at 24 hours showed corrosion beginning, with one spot on each of the five wires. Periodic observations made during two Weeks of incubation showed corrosion gradually spreading along each wire.

Five similar wires were likewise placed on medium 1089-3-3. Powdered neomycin sulfate was placed along each wire. Observations made after 24 hours showed no corrosion. After 5 days incubation 2 corrosion spots appeared. Neomycin sulfate was applied to these two corrosion spots and they subsided. Observations made periodically during two weeks of incubation showed no additional corrosion spots and the two which started did not spread.

EXAMPLE II Ten aluminum alloy wires (type 568, 5 centimeters in length) were autoclaved 2 hours at 121 C. and aseptically placed on Petri plates of medium 108933. After incubation at 2325 C. for 24 hours, 11 corrosion spots developed with two spots on one wire and one spot on each of the others. These corrosion spots spread gradually along the wires during two weeks of incubation such that significant lengths of each wire showed heavy corrosion.

Ten similar aluminum alloy wires were autoc aved for two hours and aseptically placed on Petri plates of medium 108933. Terramycin containing an equal concentration of a surface active agent (benzethonium chloride) was sprinkled on each wire. Incubation was at 23-25 C. Observations made at 24 hours showed no detectible corrosion. Observations made after 3 days of incubation showed six wires free of any corrosion and four wires each had a small spot of corrosion starting. Terramycin applied directly to these beginning corrosion spots caused the corrosion to dry up. Observations made periodically during two weeks of incubation showed that the four corrosion spots which had started, remained dormant and there was no spreading of corrosion across the wires.

EXAMPLE III Five aluminum alloy wires (type 565, 5 centimeter lengths) were autoclaved at 121 C. for 2 hours and aseptically placed on Petri plates of medium 1089-3-3. Incubation was at 2325 C. Observations made at 24 hours showed each of the wires beginning to corrode. Subsequent observations made during an incubation period of two weeks showed that the corrosion spread, covering the major portion of the wires.

Five similarly autoclaved aluminum alloy wires were aseptically placed on Petri plates of medium 1089-3-3. Ma'ndelamine was introduced into the plates by covering each wire. Observations made after 24 hours showed no corrosion. After 3 days three of the wires showed corrosion spots. Additional mandelamine was added directly to the corrosion spots. This type of corrosion was retarded but mandelamine proved to be less effective against the white corrosion than against a reddish type causing mild pitting. Consequently, terramycin containing an equal concentration of a surface active agent (benzethonium chloride) was added. Penetration into the corrosion spots appeared quite effective and within 6 hours all corrosion activity had subsided. Observations made during the remaining part of a two-week incubation period showed that all corrosion had dried up and did not spread across the wires as in the non-treated controls.

10 EXAMPLE 1v Two aluminum wires autoclaved 2 hours at 121 C. were aseptically placed on a Petri dish of medium 1089- 3-3. After 24 hours, corrosion started on each wire. Periodic observations made during a two-week incubation period showed the corrosion spread across most of the length of each wire.

Two aluminum wires similarly autoclaved were placed on medium l0893-3. Potassium penicillin G was sprinkled over each wire. After 24 hours of incubation, no corrosion was detected. Periodic observations made during a two-week incubation period showed no corrosion.

EXAMPLE V Five aluminum wires autoclaved 2 hours at 121 C. were aseptically placed on Petri plates of medium 1089- 3-3. Observations made at 24 hours showed corrosion developing on each wire. Periodic observations made during a two-week incubation period showed that the corrosion gradually spread across most of the wire length on each wire.

A Petri plate of medium 1089-3-3 was inoculated with fungus 1089-4-2B and incubated 3 days at 23-25 C. Five aluminum wires were autoclaved 2 hours at 121 C. and aseptically placed on the plates and no corrosion developed after 15 additional days of incubation.

Two Petri dishes of medium 1089-3-3 were inoculated with fungus 1089-4-2B and at the same time, before antibiotics were produced, 5 aluminum wires previously autoclaved 2 hours at 121 C. were aseptically introduced into each plate. Six of the ten wires showed corrosion slowly develop after 4 days.

Ten additional wires were introduced (5 into each plate, between the other wires) after the fungus had developed for 3 days and produced antibiotics. None of the wires introduced after antibiotic production subsequently corroded during a 16-day incubation period, indicating the necessity for the antibiotic to be present initially in order to effectively inhibit corrosion.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to the preferred embodiments, it will be understood that various omissions and substitutions and changes in the form and details of the described embodiments and in their operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. A process for inhibiting metal corrosion comprising applying to a metal substrate subject to such corrosion, a composition selected from the group comprising terramycin, neomycin or mandelamine, said metal being selected from the group consisting of aluminum, iron, c0p per and zinc.

2. A method for inhibiting the corrosion of metals which is due to the presence of autotrophic agents, which comprises applying to the metal so subject to corrosion by such agents a composition selected from the group consisting of terramycin, neomycin and mandelamine, said metal being selected from the group consisting of aluminum, iron, copper and zinc.

3. A method of inhibiting autotrophic agent-produced corrosion of a metal selected from the group consisting of aluminum, iron, copper and zinc which comprises forming a protective coating material by including therein a composition selected from the group consisting of terramycin, neomycin and mandelamine, and applying a layer of such protective coating material to a substrate formed of said metal in an amount sufficient to inhibit growth of said agents.

4. A method according to claim 3, wherein the substrate is a pipe.

5. A method according to claim 3, wherein the substrate is a wire.

6. A corrodible metal substrate having a coating adhered thereon for inhibiting the corrosion of said object, Where the corrosion is produced by the activity of autotrophic agents said coating comprising a composition selected from the group consisting of terramycin, neomycin and mandelamine in an amount sufiicient to inhibit efiectively the growth of such agents and said metal being selected from the group consisting of aluminum, iron, copper and zinc.

7. An article according to claim 6, wherein the substrate is a Wire.

8. The method of claim 2 wherein the metal is in the form of a pipe or a wire.

References Cited UNITED STATES PATENTS JULIUS FROME, Primary Examiner T. MORRIS, Assistant Examiner U.S. C1. X.R.

2l-2.5; l06-14; l17127, 128; 252-387 

